1. Field of the Invention
The present invention relates generally to an extrusion method and apparatus, and more particularly, to an apparatus and process for preparing a thermoplastic resin composition such as a hot melt composition.
2. Description of the Prior Art
Heretofore, uniaxial screw type extruders have been employed which extrude molten thermoplastic resins. However, in the blending of two or more components, it is not sufficient to merely blend the components in a conventional uniaxial screw type extruder, and there is an increased need for thermoplastic resin compositions, such as hot melt compositions. However, it is impossible to prepare such thermoplastic resin compositions especially hot melt compositions, by employing the conventional extruders because of the low blendability or slip of the molten thermoplastic resin.
Accordingly, thermoplastic resin compositions, such as hot melt compositions, have been prepared by melting raw materials in a heated kneader equipped with a stirrer, and then extruding the mixture through a heated tube by means of a pump. A large-sized apparatus has been employed, and thermal deterioration of the components of the compositions have occurred because of the long term heating processes involved.
An example of a conventional extruder useful for extruding thermoplastic resin compositions is one which comprises a hopper, a melting cylinder, a cylinder heating mechanism, and a screw portion in the cylinder. When the extruder is used to extrude a low viscosity resin composition, such as a hot melt composition, the molten composition slips into the cylinder through means of a screw which rotates in the cylinder, however, complete mixing, kneading and extruding of the compositions are not achieved by such a conventional extruder.